DESCRIPTION: The long term objectives of the proposed studies are to determine whether there are sinusoidal magnetic field (MF) exposure paradigms which reproducibly alter the production of pineal melatonin and its secretion into the blood, to define the MF exposure parameters that are critical to the melatonin response, and to investigate the biophysical mechanisms whereby the pineal gland responds to MF fields.To meet these objectives, they will examine the reliability of what has come to be known as the Yellon MF exposure paradigm (short term daytime exposure to sinusoidal MF) in inducing a decrease in pineal melatonin production and secretion on the night following the MF exposure. They will also determine the efficacy of short term nighttime exposures to 60 Hz MF in changing the synthesis and release of melatonin. For both of these exposure paradigms, they plan to establish response thresholds for field strength and duration of exposure and, if possible, dose-response relationships. When magnetic field exposures are done at night, light exposed (which rapidly depresses pineal melatonin) positive controls will be included for comparison. The endpoints in all studies will be pineal and blood melatonin levels as well as the activities of enzymes related to melatonin production. After a reproducible model is identified, they will test whether the ability of sinusoidal MF to reduce melatonin production is a consequence of the fields acting directly on the pineal gland. Finally, they will examine the possibility that the eyes, the biological clock in the hypothalamus (the suprachiasmatic nuclei or SCN), and the peripheral sympathetic nervous system serve in MF perception and, in so doing, alter the circadian melatonin cycle. Since melatonin is a natural oncostatic agent, the depressed levels of the hormone which follow certain MF exposures may be related to the alleged increased cancer incidence in individuals living or working in higher than usual background electromagnetic fields, e.g., in the vicinity of high power lines.